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CONTENTS
Volume 29, Number 6, December 2025
 

Abstract
Fluid viscous dampers have become increasingly significant in the seismic design and rehabilitation of structures, as these devices can reduce both the response and damage of a structure. In this regard, it is crucial to evaluate the distribution and configuration of these devices within the structure. This paper examines several configurations of linear and non-linear fluid viscous dampers using three steel frames of 9, 16, and 20-storeys subjected to soft-soil earthquakes, such as those affecting the Valley of Mexico City. To evaluate the damper configurations, the seismic performance of the upgraded frames with different damper arrangements is assessed, considering various ratios of supplementary damping. The results indicate that the scissor-type configuration and storey shear strain energy distribution reduce the structural response by up to 80% compared to the diagonal configuration in the studied models.

Key Words
damper configuration; damping coefficient distribution; nonlinear fluid viscous dampers; nonlinear time history analysis

Address
Francisco Bañuelos-García, Jaime De La Colina and David De-León-Escobedo: Facultad de Ingeniería, Universidad Autónoma del Estado de México, Cerro de Coatepec S/N, Ciudad Universitaria, Toluca 50110, Mexico
Marco Escamilla-García: Instituto de Ciencias Básicas e Ingeniería, Universidad Autónoma del Estado de Hidalgo, km 4.5 carretera Pachuca-Tulancingo S/N, Mineral de la Reforma 42184, Hidalgo, México

Abstract
Ground acceleration response spectrum prediction plays a crucial role in seismic design for engineering structures. Conventional one-dimensional site response analysis methods often fail to simulate complex sites and dynamic soil processes accurately and with strong uncertainty, resulting in notable discrepancies between computed and measured response spectra. Leveraging seismic records from 2428 ground motion measurements at 43 horizontal site stations in the KiK-net database, a predictive model BO-XGBR-SS was developed based on Extreme Gradient Boosting (XGBoost). By disregarding constitutive assumptions and utilizing bedrock input and site information as training features, ensemble learning algorithms (XGBoost and Random Forest) were employed for model training, complemented by Bayesian optimization based on Gaussian processes for hyperparameter tuning. Comparisons show XGBoost performs better, prompting further enhancement through a stratified sampling training strategy guided by site categories to mitigate potential feature imbalances. Mean square error (MSE), Coefficient of determination (R2), Pearson correlation coefficient (R), spectral acceleration residual variability and residual probability distribution were used as the evaluation parameters. The average prediction error of the proposed model is reduced by more than 30% compared to the equivalent linear and nonlinear methods. Furthermore, the matching accuracy of each response spectrum prediction is analyzed using Dynamic Time Warping (DTW) to combine normalized response spectra and typical records, and the proposed BO-XGBR-SS model performs stably under a variety of site conditions, overcoming the shortcomings of high-frequency underestimation and anomalous amplification of the long-period response spectra in the one-dimensional site-response analysis methods. The model's generalization ability was validated using recent seismic motion records as an external dataset. Feature interpretation using SHAP analysis aligned with existing knowledge, affirming the model's effective capture of correlations between features and seismic response.

Key Words
DTW; explainability; ground acceleration response spectrum; machine learning; site category

Address
1) Key Laboratory of Earthquake Engineering and Engineering Vibration, Institute of Engineering Mechanics, China Earthquake Administration, Harbin 150080, China, 2) Key Laboratory of Earthquake Disaster Mitigation, Ministry of Emergency Management, Harbin 150080, China

Abstract
Seismic isolation offers a simple and direct opportunity to control or even eliminate damage to structures subjected to ground shaking by simultaneously reducing deformations and acceleration demands. A base isolation system decouples the superstructure from the ground resulting in elongation of fundamental period of the structure and reducing the accelerations transferred to superstructure during ground shaking. However, increasing the fundamental period of the structure is mostly accompanied by increased displacement demands. In base isolated structures, this large displacement is concentrated at base level where seismic isolation devices are installed and designed to handle these large deformations without damage. A typical base isolated basement design requires a space in which the building is free to move sideways without hitting the surrounding structure. For this challenge, a sufficient separation distance between structures is logically considered to allow moving base of buildings. Nowadays, in order to mitigate impact force and increase energy absorption, rubber bumpers are widely used within contact zone of base level of isolated structures to dissipate energy and control base displacement. Bumpers are typically included special spring and damper, which control the value of impact force and dissipated energy during collisions. In this paper, through numerical simulation based on the results of experimental test, an impact is parametrically simulated and hysteresis loop of impact is mathematically calibrated. The aim of this study is to focus on the effect of damper to create a novel equation in order to calculate the value of damping using all effective parameters for square shape of rubber bumpers. The new formula is normally solved to determine the value of damping and the accuracy of the equation is investigated by the validation of numerical results against experimental results. The results of the study indicate that rubber bumper can mitigate the value of transferred impact force by absorbing energy during impact while the number of collisions is physically increased. In fact, using rubber bumper as an external element can be an accepted method to decrease negative effect of seismic excitations for base isolation system.

Key Words
bumper; damping; earthquake; impact; pounding

Address
Department of Civil Engineering, Se.C., Islamic Azad Univerity, Semnan, Iran

Abstract
The influence of low-frequency contents in seismic waves on torsional response of frames remains systematically unelucidated. Based on structural dynamics theory, this study uses time-history analysis to investigate the effects of low-frequency contents on frame torsional response under earthquake wave passage excitations. Three-dimensional numerical models of planar regular (RFSs) and irregular (IFSs) frames were developed in ABAQUS. By applying wave passage excitations with varying low-frequency contents, peak shear forces in first story corner columns along the excitation direction were calculated. Results show that with sufficient low-frequency contents, peak shear forces in outer corner columns of RFSs and IFSs increase by 31.6% and 85.3%, respectively, under frequent earthquakes. Under rare earthquakes, the corner columns on the wave-facing direction of RFSs and IFSs exhibit 17.9% and 33.9% increases in peak shear forces. These findings indicate that when seismic waves at low-frequency contents are sufficient, the corner columns of RFSs and the outer corner columns of IFSs are susceptible to wave passage effect under frequent earthquakes, while the corner columns on the wave-facing direction of both RFSs and IFSs are susceptible to wave passage effect under rare earthquakes. However, when the low-frequency content is insufficient, the corner columns do not exhibit this effect.

Key Words
earthquake wave passage excitation; frequent earthquake; low-frequency contents; planar irregular frame structures; rare earthquake; torsional response

Address
School of Civil Engineering, Shenyang Jianzhu University, Shenyang 110168, Liaoning Province, China

Abstract
In geotechnical studies, liquefaction is an important phenomenon of mechanical instability. This mechanism has been constantly modified to include new parameters that can control the mechanical instability under vibratory stresses to avoid catastrophic failure of the soil (such instability can manifest itself in serious damage with large displacements). In this work, the objective is to follow the vertical displacement of an intruder on a saturated sandy soil and the variation of the relative density after test. It is possible to demonstrate an alternative liquefaction mechanism by using two reduced models without and with inclusions and geotextile as reinforcement: the vibratory accelerations are under BOUMERDES2003 model earthquakes with reduction of their intensity to 10-3, variation of this intensity between 5.10-4 and 3.10-3 and the variation of the degrees of saturation from 50% to 100%. The sample is subjected to a seismic shock was shown that different behavior has a direct effect on the vertical displacement of the intruder, it was concluded that the imposed seismic acceleration and the relative density of the soil determine the vertical displacement of the intruder into the sample. Finally, it's important to develop that the vertical displacement of the intruder and the final relative density have a direct relation with this phenomenon.

Key Words
instability; intruder; liquefaction; saturated sandy soil; seismic shock

Address
Mohammed Bousmaha: Materials, Soils and Thermal Laboratory, University of Science and Technology of Mohammed Boudiaf of Oran, Algeria
Mohamed Bensoula: Laboratory of Construction, Transports and Environment Protection (LCTPE), University Abdelhamid Ibn Badis of Mostaganem, Algeria

Abstract
Continuously reinforced concrete pavements (CRCPs) are known for their excellent long-term durability; however, the absence of joints can lead to critical cracking depending on the mixture design, potentially degrading their performance. Therefore, this study aimed to investigate the fatigue performance of a CRCP with various binder compositions, such as ordinary Portland cement, fly ash, and expansive additives (EA), under harsh environmental conditions. A multi-scale chemo-hygral computational system (DuCOM-COM3) was employed to simulate the damage caused by shrinkage under actual temperature and humidity variations as well as the long-term fatigue performance under cyclic wheel loading. The computational system integrates models for cement hydration, pore structure development, moisture transport, expansive pressure owing to EA, and time-dependent constitutive laws for structural analysis, enabling a comprehensive analysis of the drying shrinkage and stress-strain behavior of concrete under cyclic fatigue loading. Using this approach, the effects of binder composition and the advantages of EAs on the long-term fatigue performance were quantitatively evaluated, and the suitability of mixture designs for enhancing the durability of CRCPs was investigated in detail.

Key Words
continuously reinforced concrete pavement; expansive additive; fatigue; fly ash; multi-scale analysis

Address
Department of Civil Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyou-ku, Tokyo, Japan

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